The generator stator core is the largest monobloc component in the train of a turbine generator set. Stator cores are manufactured from thousands of thin steel laminations which are stacked, pressed and clamped together into the large cylindrical form of the stator core. Clamping is necessary for several reasons but principally to ensure that geometric form is maintained under the forces imposed during unit operation. Improper clamping can result in lamination vibration during generator operation, due to magnetic impulses and/or core elliptical dilation.
Typically, the stator core is assembled at the final installation site. However, the large size of the stator core results in stator core manufacturing complexities, including the need for generous floor space, high crane requirements, manufacturing lead time and other associated manufacturing difficulties. For example, if the core is stacked directly in the stator frame, the frame must be delivered to the site before any manufacturing steps can occur. Additionally, intermediate core pressing equipment is needed to press and clamp the laminations together at incremental lengths. If, on the other hand, the stator core is manufactured in an external fixture, the external fixture itself adds to the manufacturing costs and requires additional floor space on site and still requires the use of heavy cranes.
U.S. Pat. No. 5,875,540 by Sargeant, which is incorporated herein by reference, overcame some of the problems with the prior art by first assembling a number of laminations into a distinct set, referred to as a donut, and then stacking these donuts to form a stator core. This saved great amounts of assembly time compared to assembling the laminations individually, and produced a stator core with less flaws.
When the individual laminations, or the set of laminations in a donut, are installed into a core, they engage what are referred to as keybars. Keybars are essentially rods that run the internal length of the stator core and provide a hook-in spot for the laminations. FIG. 1 illustrates a stator frame that is empty of any laminations. The keybars 6 run the internal length of the stator frame 2, and are generally attached to the frame through stator support rings 4.
The prior art requires that the laminations and donuts be stacked vertically, using gravity to guide the donuts into place. This can lead to large scale rearrangement and imposition of the stator core and surrounding area for substantial periods of time. Using the prior art, stacking a core horizontally is extremely difficult with lamination aggregates, and large aggregates, such as donuts, is essentially precluded. What is needed is a method and apparatus for stacking laminations and donuts horizontally. This is particularly needed in pre-existing stator frames, not initially designed for such assemblies, where vertical stacking is not practicable and where room is otherwise limited.